The document discusses programmable logic controllers (PLCs). It defines PLCs as digitally operating electronic devices that use programmable memory to implement logic functions to control machines and processes through digital and analog inputs and outputs. The document outlines the history and evolution of PLCs from relay-based to solid-state designs. It describes typical PLC architectures, components, programming languages like ladder logic, applications in machine control and other industrial processes, and advantages of PLCs over traditional electromechanical controls.

1. PROGRAMMABLE LOGIC
CONTROLLER
L. SUDHA
CMTI

2. PLC Introduction
Controller
Programmable
Logic
Defined by National Electrical Manufacturers Association (NEMA) in 1978
“ A Digitally operating electronic apparatus which uses a programmable memory for the storage of
instructions for implementing specific functions, such as logic, sequencing, timing, counting and
arithmetic to control through Digital or Analogue Input / Outputs, various types of machines or
process

3. SIEMENS

4. Fanuc PLC & Panel

5. Advantages of PLC
Cost effective for controlling complex
systems.
Flexible and can be reapplied to control
other systems quickly and easily.
Computational abilities allow more
sophisticated control.
Trouble shooting aids make programming
easier and reduce downtime.
Reliable components make these likely to
operate for years before failure.

6. PLC APPLICATIONS
• Machine control
• Process control
• Automated product quality
inspection
• Data acquisition
• Material handling
• Sorters,packing lines, wrappers

7. Subsystems of a CNC system
Servo
HMI
MMI
PLC
(INTEGRATED)
PMC / PMI / PC

8. Relay

9. 12/13/2022
SOLID STATE RELAYS

10. Generation of PLCs
Program based
(Software)
Relay Based
Circuit
IC based
Solid State

11. NC-PLC window
NC
PLC
Part
Program
M
S
T
I / Os
MMC
status
Servo
status
Interlocks
Program
execution
status

12. Role of a PLC
Part Program
Input devices
Output devices
•Digital
– Pushbuttons, limit switches
– Sensors, selectorswitches
•Analog devices
–Voltage or current inputs 0-100mA
and converts to digital information
–Flow meters,
–Pressure transducers,
–Thermocouples
Output Devices
• Digital devices
– Lights,leds, relay, small motors
• Analog devices
– Converts D to A
– 0-10V or 4-20mA
– Position control
– Flow control
– Pressure regulator
Part Program
O0110
N001 G90 ; Absolute coordinate system
N002 M06 T01 ; Select tool #1 (turning tool)
N003 M03 S2000 ; Turn spindle on (CW), set 2000 rpm
N004 G00 X0.0 Z-0.9 ; Rapid traverse
N005 G01 X0.0 Z-1.0 F10 ; enter part
N006 G01 X1.0 ; make facing cut
N007 G01 Z-3.9 ; turn side
N008 M30 ; end of program

13. PLC ARCHITECTURE
PROGRAMMER
PROGRAM
MEMORY
INPUT
MODULE CPU
OUTPUT
MODULE
INPUTS OUTPUTS
PLC
DATA
MEMORY
PC / HAND HELD UNIT

14. PLC ARCHITECTURE Contd
INPUT
IMAGE
TABLE
OUTPUT
IMAGE
TABLE
LOGIC
DIO DIO
INPUTS OUTPUTS
OP
&
NC
OP
&
NC

15. Electrical Connectivity to External World
Input Devices
Output Devices
24 V 5 V
5 V 24 V
Optical Isolation
Optical Isolation

16. Machine Tool Functionality handled by PLC
PLC
Turret / ATC
Tailstock & Quill
Chuck
Spindle Gear change, etc.
Chip Conveyer
Lubrication
Coolant
Machine Tool Interlock

17. Scanning Cycle
Read Inputs
Run Internal Diags
Execute Logic
Update outputs
Outputs
• Timer, Counters
• LED
• Solenoid
Inputs
 Push Button
 Sensor
 Limit switch
 Fast Input !
 Emergency
 Probe Input
 Over travel Limit (NC controls)

18. FAST INPUTS
• CRITICAL INPUTS LIKE OVER TRAVEL LIMIT SWITCHES,
EMERGENCY STOP ARE FAST INPUTS TO PLC
• FAST INPUTS ARE GENERALLY CONNECTED WITH NC
CONTACTS
• TIME / INTERRUPT BASED SCANNING

19. Timers
ON Delay Timer
OFF Delay Timer
Pulse Timer
Extended Pulse Timer
Enable
Output
Delay
Output
Delay
Enable
Enable
Output
Delay
Delay
Enable
Output

20. Counters
Enable
Event
Output
Types of Counters
1. UP Counter
2. DOWN Counter
3. UPDOWN Counter

21. DIGITAL OUTPUT MODULES
OUTPUT
MODULE
24V DC
LOAD
OUTPUT
MODULE
LOAD
24V GND
SINKING TYPE SOURCING TYPE

22. OUTPUT MODULES Contd
OUTPUT
MODULE
24V GND
24V DC
24V GND
LOAD
RELAY
RELAY TYPE

23. Miscellaneous Codes
Postlude
M-Code
Prelude
M03: Spindle CW
M04: Spindle CCW
M08: Coolant ON
•
•
•
•
M05: Spindle stop
M09: Coolant OFF

24. MST Codes
NC PLC
MST Execution
MST Codes

25. Programming Languages
1. Ladder
2. Statement List
3. Flow Chart
4. HLL – High Level Language
IEC-1131-3 is the PLC programming Standard for Exchangeability

26. Ladder Programming
• Ladder is one of the powerful
ways of programming
• It is also known as Universal
Programming Language
• Standard for all PLCs from
different manufacturers

27. Program Devices and Loading
PC based
Program
Ehternet /
Memory Card

28. PROCEDURAL STEPS
1. Define the process
2. List out the sensors (Input & Output)
3. Assign the PLC I/O numbers
4. Build the logic’s
5. Key in the program into the PLC (Download if
program is developed in a Personal Computer)
6. Check the logic by forcing the inputs
7. Use I/O simulator and check the logic
8. Check the logic for various conditions of input
9. Make modifications if required and try again

29. Important points to remember during
Ladder Programming
• Logic is always executed from Left to Right and Top to Bottom.
The Input side of the Logic is executed first before executing
the Output side logic.
• All Internal Flags (Except Retentive Flags) are initialized to ‘0’
on power up.
• All Outputs are initialized to ‘0’ on power up.
• Output Flags can be used in the Input side, but not vice-versa.
• For a particular input either NO or NC symbol can be placed in
the Logic irrespective of the type of Contact used in Input.
• All logical sequences are generally a combination of AND, OR
and NOT logic’s only.

30. NOT GATE
The ladder logic equivalent for a NOT function looks like a
normal contact but with a slash through it.
Input A Output
0 1
1 0
The simplest of all logic functions is the NOT gate.

31. AND GATE Input A Input B Output
0 0 0
1 0 0
0 1 0
1 1 1

32. OR GATE Input A Input B Output
0 0 0
1 0 1
0 1 1
1 1 1

33. NOR GATE Input A Input B Output
0 0 1
1 0 0
0 1 0
1 1 0

34. NAND GATE
Input A Input B Output
0 0 1
1 0 1
0 1 1
1 1 0

35. XOR GATE
Input A Input B Output
0 0 0
1 0 1
0 1 1
1 1 0

36. XNOR GATE
Input A Input B Output
0 0 1
1 0 0
0 1 0
1 1 1

37. Logical Instructions
AND Logic
OR Logic
I1.0 I2.0 O1.0
I1.0 O1.0
I2.0
Latch
I1.0 O1.0
O1.0

38. DIGITAL IO SPECS
• NO OF INPUTS : 8/16/32
• INPUT TYPE : SOURCING / SINKING
• INPUT VOLTAGE : 10-32VDC
• INPUT TURN ON LEVEL – 8VDC,@2.3mADC
MINIMUM
• INPUT TURN OFF LEVEL –
2.5VDC@0.05maADC MAXIMUM
• INPUT SOURCE : 5VDC FROM
CONTROLLER

39. I/O Devices

40. Selection of PLCs
The points to be remembered while selecting PLC are as follows:
1. No. of Inputs / Outputs the PLC can handle
2. Type of Inputs / Outputs supported
3. No. of Timers / Counters available
4. Types of Counters / Timers available
5. Scan time per K of the PLC
6. PLC memory capacity
7. Fast / Interrupt Input and Power On scan
8. Proramming languages supported
9. Programming devices supported
10. Diagnostic features like Forcing function and Power Flow Diagram
11. Axes Control supported with PID algorithmn
12. Any Networking capability available
13. Special functions like Turret / ATC macros supported
14. Arithmetic / Boolean Instruction set
15. Isolation of Inputs / Outputs from PLC
16. Watch dog Timer

41. Logical Instructions
AND Logic
OR Logic
I1.0 I2.0 O1.0
I1.0 O1.0
I2.0
Latch
I1.0 O1.0
O1.0
Single Shot
I1.0 F1.0
F2.0
F2.0

42. Logical instructions Contd
Oscillator
F2.0 F2.0
O1.0
I1.0 O1.0
O1.0
Latch with Unlatch (Motor ON / OFF)
I2.0
I1.0 O1.0
O1.0
I2.0

43. Thank You